JPS61151466A - Method for measuring moving speed of matter - Google Patents

Abstract

PURPOSE:To make it possible to measure the speed of moving matter with high accuracy, by arranging moving matter to the waist region of coherent light to irradiate the moving matter with coherent light and arranging a light receiving element so as to leave a specific distance from the moving matter. CONSTITUTION:A numeral 11 is a coherent laser beam source and anumeral 12 is a projection optical system for converting laser beam to a converging region, a waist region and a diffusion region and a numeral 13 is pervious moving matter which is arranged to the converging region and moves at a speed V and a numeral 14 is a photoelectric converter element which is arranged to a laser beam region. Because the photoelectric converter element 14 is arranged at a position spaced apart by R>=(piW0)/lambda from the moving matter 13, a speckle is brought to a boiling state on the surface of a perforated plate 16 and the highly accurate measurement of a speed is enabled. Herein, lambda is the wavelength of laser beam and w0 is a waist radius.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field This invention irradiates a moving object with coherent light such as a laser beam, and utilizes the resulting random interference pattern (speckle pattern) to This invention relates to a method for measuring the moving speed of a person.

(b) Prior Art Generally, as shown in FIG. 3, when a moving object 4 is irradiated with coherent light 3 from a laser light source 1 through a projection optical system 2, the light transmitted or reflected by the moving object 4 is When received at the light receiving point 5, the speckle pattern undergoes two movements: translation movement and boiling movement (the speckle does not move, but the intensity of the light changes and oscillates on the spot). It is known that the pattern moves and displaces (Magazine "Laser Research" Vol. 8 No. 2, No. 8)
Volume No. 3). In the figure, at the light receiving point 5, the normalized autocorrelation function r(τ.

ν) is σ#1+□・・・・・・(2) Tonaru.

The above (Equation 11) shows that the autocorrelation function attenuates as the object speed V increases, and for example, the correlation is 1/
If the time at which e is reached is τC (autocorrelation length), then from equation (1).

a: Radius of socket opening. The speed (2) can be measured using this τC, and the inventors of this application have already filed an application for a speckle speedometer employing this principle (Japanese Patent Application No. 54043/1982).

Also, the number N of zero crossings per unit time of light fluctuation.

is also calculated from equation (1) above, and becomes: The speed ■ can also be measured by counting this zero-crossing number No. The inventors of this application have already filed an application for a speckle speedometer that adopts this principle (Utility Application No. 106376/1983). , special training 1982-
No. 54041).

All of the above-mentioned speckle velocimeters that have already been filed employ illumination methods using converging beams or expanding beams.

(c) Problems to be solved by the invention The conventional speckle velocity meter described above uses a convergent beam or an expanded beam for illumination, and measures the speed based on the above formula (3) or (4). Therefore, if the roughness correlation length of the rough object is relatively long compared to the illumination area, the speckles will be non-Gaussian, and for paper etc., the speckles will become smaller due to the bleeding phenomenon, and the speckles will be normal. This method has the drawback that speckles with no size are formed, which changes the autocorrelation function of light fluctuations, making it impossible to perform accurate measurements. Further, when the object to be measured changes, for example from copper to paper to cloth, ΔX changes depending on the object to be measured, and therefore the signal processing section has to make corrections for each change in object. Furthermore, if the illumination beam is not a perfect spherical wave but contains wavefront aberration, the translation of speckles is strongly related to the wavefront curvature, making the translation unstable, which also has the disadvantage of reducing measurement accuracy. there were.

In view of the above, the present invention provides an object moving speed that allows the speed of the object to be measured with high accuracy even when the speckle becomes non-Gaussian, when the measurement object is changed, and even when the illumination beam contains wavefront aberration. The purpose is to provide a measurement method.

(d) Means and operation for solving the problems In order to solve the above problems, the present invention makes speckles boil on the light-receiving surface. The optical arrangement that causes speckle boiling is when the measurement object is placed in the waist region of coherent light, which has a convergence region, a waist region, and a diffusion region, and the light receiving surface is placed from the object to the diffusion region, and the measurement object is placed in the convergence region, Although it is conceivable that the light-receiving surface may be arranged in the waist region, the present invention adopts the latter arrangement. That is, the method for measuring the speed of an object according to the present invention includes arranging a moving object in a waist region of coherent light emitted from a light source, and irradiating the moving object with the coherent light.
A light-receiving element is provided at a distance of R=πW0'/λ (λ: laser beam wavelength, wo: waist radius) or more from the moving object, and the speckle pattern obtained by this light-receiving element is processed by a signal processing unit to calculate the moving speed. I try to measure it.

In this movement measurement method, since R=-ρ in the convergence region, R/ρ=-1, and from the above equation (2), the translational magnification ρ=O. Therefore, the burial mounds of formulas (3) and (4) are O. Therefore, the cross-correlation length τC1 zero crossover number No.
is V π , and even if ΔX, ρ, etc. fluctuate, the measurement results are not affected.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a schematic diagram of a laser speckle velocimeter in which the present invention is implemented. In the figure, 11 is a laser light source that emits a coherent beam, and 12 is a laser light source 1.
This is a light projecting optical system that converts a beam of light from one direction into a light beam having a convergence region, a waist region, and a diffusion region. Reference numeral 13 denotes a transparent moving object, which is placed in the convergence region and is moving in a direction perpendicular to the light beam at a speed of ■. 14 is a photoelectric conversion element, for example, a phototube or a semiconductor light receiving element is used. This photoelectric conversion element 14 is arranged in the waist region of the light beam. An aperture plate 16 with pinhole apertures 15 is provided in front of the photoelectric element 14 . Further, a signal processing section 17 for processing the converted speckle pattern signal is connected to the photoelectric conversion element 14.

As shown in FIG. 2, this signal processing section 17 includes a broadband amplifier 18 that amplifies the speckle pattern signal from the photoelectric conversion element 14, and a DC component removal circuit 19 that cuts the DC component from the amplified speckle pattern signal. , further comprising a Schmitt trigger circuit 20, a one-shot multi-circuit 21, a counter circuit 22, and a clock circuit 23.

In the laser speckle velocimeter of this embodiment, when a laser beam is emitted from a laser light source 11, it is converted into a light beam (preferably a Gaussian beam) by a projection optical system 12. In this case, the beam waist radius W0 is as follows, where the wavelength is λ.

Since the photoelectric conversion element 14 is provided at the beam waist and the moving object 13 is placed at the position of λ, that is, in the convergence region,
Assuming that R=-ρ and σ=O, and the object to be measured 13 is moving at a speed of ■, speckles become boiling on the surface of the aperture plate 16 and fluctuate over time.

This fluctuation signal is converted into an electrical signal by the photoelectric conversion element 14 and input to the signal processing section 17 . The speed of the change at this time is proportional to the moving speed V of the object 13, and the speed of this change is detected by the signal processing section 17.

In the signal processing section 17, first, the speckle signal (fluctuation signal) converted into an electric signal is amplified to a predetermined level by a broadband amplifier 18, and the amplified signal is further passed through a DC component removal circuit 19 for zero-crossing detection. The DC component is cut off, and the Schmitt trigger circuit 20 creates a pulse train in which high and low are reversed at the time of zero crossing. This pulse train is shaped into a predetermined pulse width by the one-shot multi-circuit 21, and the number of zero-crossing counts per unit time is determined by the counter circuit 22.
/2 is counted. This zero crossing number No is as shown in equation (4) as a general theoretical equation, but in this example, since the light is received in a boiling state, the burial mound in equation (4) can be ignored, and it becomes π W . Therefore, the count value of the counting circuit 22 is not affected by the speckle size ΔX, the aperture area a, the distance R between the object and the photoelectric conversion element, and the wavefront curvature ρ of the beam, even if the material of the object 13 is changed. , ΔX change, or even if there is distortion in the wavefront curvature ρ, these effects do not affect the speed measurement and there is no need for any correction.

In the above embodiment, a zero-crossing number detection circuit is used as an example of the signal processing unit 17, but the present invention is not limited to this, and a circuit for calculating the autocorrelation length τC may also be used.

(f) Effects of the Invention According to the present invention, speed measurement is performed by processing signals received in the boiling state of speckles.
Since speckle size and wavefront curvature do not affect measurement results, highly accurate measurements can be performed. Further, even if the object to be measured is changed during the process, the measurement can be continued without any correction.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a laser speckle velocimeter in which the present invention is implemented, Fig. 2 is a circuit diagram showing a specific example of the signal processing section of the laser speckle velocimeter, and Fig. 3 is a schematic diagram of a conventional laser speckle velocimeter. FIG. 3 is a diagram showing an optical arrangement for explaining speed measurement using laser speckles. ll: Laser light source, 12: Light projecting optical system, 13: Moving object, 14: Photoelectric conversion element, 17: Signal processing unit. Patent applicant Tateishi Electric Co., Ltd. Agent
Patent Attorney Shigeru Nakamura Figure 1 ■ ] 6 Figure 2

Claims (1)

[Claims] (1) Coherent light from a light source is converged by an optical system,
converting the light beam into a light beam having a waist region and a diffusion region, providing a photoelectric conversion element in the waist region, arranging a moving object in the convergence region, irradiating the light beam onto the moving object, and irradiating the light beam onto the photoelectric conversion element. A method for measuring the moving speed of an object in which the obtained speckle pattern signal is processed by a signal processing unit to measure the moving speed.